With the explosion of the Internet in recent years, an increasing amount of valuable information has become available online. The Internet has become a global community, rich with resources and communications facilities. However, the Internet is also a frontier that remains largely unregulated, and hence contains many instances of harmful or objectionable material. For example, web sites containing violent or pornographic materials are common, as are sites advocating extremist viewpoints. Additionally, perusers of the Internet are often bombarded with unsolicited advertising that they may find annoying or offensive.
Accordingly, it is often desirable to filter the content that may be retrieved from the Internet. For example, a parent or teacher may wish to prevent a child from viewing materials on violent, pornographic, or bigoted sites. Additionally, users may wish to avoid the receipt of unsolicited advertisements contained within a page being viewed. Certain schemes to effect content filtering are known. For example, Net Nanny® resides on a personal computer (PC) client and works by checking intended URL's with a local list of URL's corresponding to disallowed sites. If the intended URL is on the list, the user is denied access to the site.
Most PC's and other client computers are not connected directly to the Internet. Such computers may instead be linked to the Internet through a router, or “gateway.” For example, an Internet service provider may provide Internet access for a home computer through a shared connection. Additionally, some computers, especially those in a commercial environment, reside on a local area network (LAN), which is connected to the Internet through a gateway, which may be a firewall as well.
The placement of the gateway between the LAN, or the home computer, and the Internet has allowed for content filtering by way of what has come to be known as a “proxy server.” Also called an application level gateway, a proxy server is essentially an application that intervenes between a sender and a receiver. Proxy servers generally employ network address translation (NAT), a technique which presents a single IP address to the Internet regardless of which particular computer behind the server sent the message. Thus, the proxy server directs all user requests to the Internet as if they were coming from a single IP address, and distributes responses back to the appropriate users.
FIG. 1 illustrates the functionality of a typical proxy server when used for content filtering. As shown, a client 200 transmits a packet for a connection to a URL on the Internet to a gateway 204. In addition to other functions such as address translation and protocol compliance, the gateway 204 instantiates an application level proxy 206 connected to the client via a connection 212. The proxy 206 may contact a local or remote database 208 of disallowed sites to determine whether the requested URL corresponds to a disallowed site. If so, the connection is refused; if the requested URL does not correspond to a disallowed site, the proxy 206 establishes a connection 214 to the remote server 210 corresponding to the requested URL. During the same session, subsequent transmissions are passed by the proxy 206 between the connections 212 and 214.
The proxy server suffers many shortcomings as a means of filtering Internet content. Most importantly, use of a proxy server is slow, given that time must be spent to instantiate the proper proxy. Furthermore, all subsequent packets, even to a previously approved site, are still handled and passed off via the proxy, incurring additional transmission time. Additionally, the use of a proxy sever in this way often requires a reconfiguration of the client application, increasing administrative overhead for the local network.
Another system for filtering Internet content uses the PICS rating system. According to this method, a client browser is configured to first query a PICS/RSACi server regarding a requested URL. If the server indicates that the URL is not disallowed, then the browser proceeds to access the requested URL without any further intervention from the PICS/RSACi server. This system is inadequate in that it allows a clever user to bypass the filtering mechanism at the browser level without facing additional hurdles thereafter. Also, this system increases administrative and overhead costs in that it requires each client machine to be configured to provide the desired filtering communications.